Websites say that Firefox is outdated or incompatible even though it's the latest version

Some websites or add-ons require that you use a specific browser or version and then make a mistake detecting your installed version of Firefox. This can cause the following problems:

Websites will not work correctly, will report that your browser is outdated, unsupported, or incompatible, or will suggest that you upgrade your browser, even though you have the latest version of Firefox.

You are not able to install extensions or themes from the Mozilla Add-ons website because it incorrectly detects that you are using a different browser or an older Firefox version.

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Firefox is showing the wrong User Agent

If the website or add-on is compatible with your installed version of Firefox, the cause of the problem may be in your Firefox "User Agent" string, that identifies your browser type to websites. You can remedy this problem by resetting your user agent in your Firefox preference settings.

The about:config "This might void your warranty!" warning page may appear. Click I'll be careful, I promise! to continue to the about:config page.

Search for useragent by typing it into the FilterSearch field.

Right-clickHold down the Ctrl key while you click
on each of these preferences, if they exist, and select Reset from the context menu.

general.useragent.extra.firefox

general.useragent.extra.productName - where productName can be the name of some third party software (e.g. microsoftdotnet).

general.useragent.locale

general.useragent.override

general.useragent.security

After resetting your user agent, you may need to clear your cookies and cache:

At the top of the Firefox window, click on the Firefox button, go over to the History menu and select Clear Recent History....On the menu bar, click on the Tools menu, and select Clear Recent History....At the top of the Firefox window, click on the Tools menu, and select Clear Recent History....

In the Time Range to clear: drop-down, select Everything.

Click the arrow next to Details to display the list of items that can be cleared.

Select both Cookies and Cache.

Click Clear Now.

At the top of the Firefox window, click on the Firefox button, go over to the History menu and select Clear Recent History....On the menu bar, click on the History menu, and select Clear Recent History....At the top of the Firefox window, click on the History menu, and select Clear Recent History....

In the Time Range to clear: drop-down, select Everything.

Click the arrow next to Details to display the list of items that can be cleared.

Websites think that Firefox is outdated when you have the latest version

Some websites incorrectly see the latest version of Firefox as version 1 (instead of version 10 or above) and will think that Firefox is outdated, incompatible, or not supported. We are working with websites to get them to fix this. In the meantime, you may just be able to ignore the message but you should report the problem website:

At the top of the Firefox window, click the Firefox button, go over to the Help menu (For Windows XP: click the Help menu) and select Submit Feedback....At the top of the Firefox window, click the Help menu and select Submit Feedback....On the menu bar, click the Help menu and select Submit Feedback.... The Submit Your Feedback page will load in a new tab.

Click on "Firefox Made Me Sad".

On the Firefox Made Me Sad page that comes up, briefly describe the problem with the website, check the box, and enter the URL.

Click the Submit Feedback button.

Workaround for broken websites

You may be able to restore functionality by temporarily disguising Firefox as another browser. To do that, you can install the User Agent Switcher extension:

When Firefox restarts, you can disguise your Firefox user agent so that websites think you are using Firefox 9.0.1, as follows:

For Windows 7 and Vista, press the Alt key to bring up the old-style menu bar at the top of the Firefox window.

Go to the Tools menu, down to Default User Agent and then select Edit User Agents....

In the User Agent Switcher options window, click New and select New User Agent...

In the User Agent window, add a description (for example, Firefox 9), change the last number of the user agent to 9.0.1 and then click OK.

Next, go back to the Tools menu, down to Default User Agent and this time select the new user agent that you just created.

Finally, reload the page and it should work normally.

Go to the Tools menu, down to Default User Agent and then select Edit User Agents....

In the User Agent Switcher options window, click New and select New User Agent...

In the User Agent window, add a description (for example, Firefox 9), change the last number of the user agent to 9.0.1 and then click OK.

Next, go back to the Tools menu, down to Default User Agent and this time select the new user agent that you just created.

Finally, reload the page and it should work normally.

Note: User Agent Switcher will automatically restore the Default User Agent when you next close and restart Firefox. You will need to reselect the new Firefox 9 user agent, each time you restart Firefox and visit the problematic website.